1. Chapter 24: Thermodynamics
‘heat’-‘movement’

2. There’s a First For Everything
First Law of Thermodynamics
Heat is converted to another form of energy (mechanical) when added to a system
Q = ΔE + W
Heat Energy added can do 2 things
Increase Internal Energy
Cause external work to be done on the system

3. There’s a First For Everything
Law of Conservation of Energy is applied to machines
Engines are good examples

4. Second is the Best Second Law of Thermodynamics
Heat will always flow from hot object to colder object
Heat can be made to flow the other way, but only with external effort (ex: air conditioners)
Like water flowing down hill – always toward the cold from the hot

5. Second is the Best Second Law of Thermodynamics
Heat Engine converts internal energy into mechanical work
Only some of the heat can be converted to work
The rest is expelled as heat
This is why engines aren’t 100% efficient – this is why Thermodynamics was started – to improve steam engine

6. It’s Utter Chaos
Ordered energy comes in the form of electricity and gasoline
Disordered energy a byproduct of ordered energy (waste/heat)
Natural systems tend to proceed toward a state of greater disorder

7. Let’s Keep Things in Order
Entropy
Measured amount of disorder
Disorder increases;entropy increases
Work input into system decreases entropy
Think room cleaning – setting back up the dominos
Evolution?? Isn’t that order out of disorder?

8. Work decreasing Entropy Ex.
Refrigerator/Air Conditioner
Work put into system to increase order – separate cold & hot from warm
Very practical application of the entropy & reverse entropy process

9. HSW - Refrigerator Changing pressure to move energy with vapor points
Compressor
Inside coils
Outside coils
Step by step through the loop with number examples
500 calories of heat absorbed from food to vaporize cool liquid
Compress the gas to raise vaporization temperature (do 100 calories of work)
Compressed gas condenses – releasing 600 calories of energy
Liquid’s pressure is reduced by expansion valve – start over
500 calories out of the fridge – 600 calories released outside
Expansion valve

10. HSW – Refrigerator
Should you leave your refrigerator open to cool your kitchen?
NO! Will heat the kitchen,
Use ammonia – low vaporization temp, used to use freon – but at end of life all would be released – causes problems in atmosphere

11. Another First Adiabatic Processes Adiabatic form of 1st Law
Process where compression or expansion of gas results in no heat entering or leaving the system
Adiabatic form of 1st Law
 Air Temp. =  Pressure
Chinook winds, T-storms
Gas rising or falling causes temperature change

12. Four Stroke Internal Combustion Engine
Open Intake valve allows gas/air mixture to enter
Allows Piston to Move Down
Skip/do very fast unless didn’t do engine projects

13. Four Stroke Internal Combustion Engine
Piston moves up and compresses the gas

14. Four Stroke Internal Combustion Engine
Spark Plug Fires
Ignites the Mixture
Increase Temperature

15. Four Stroke Internal Combustion Engine
Gas Expands
Piston Moves Down

16. Four Stroke Internal Combustion Engine
Burned Gases Leave by Exhaust Valve

17. Big Finish First Law of Thermodynamics will always hold true
No exceptions
Quantity of Energy
Second Law of Thermodynamics
Probability
Quality of Energy
Probability – atomic collisions could cause 1 to leave hotter, but every rare